Digesting process and apparatus



Sept. 25, 1934." T; L. DUNBAR DIGESTING PROCESS AND APPARATUS Filed Sept. 5, 195:

4/5 YEA/7' v .D/G ES TER Ada $r 0 RA 6E TANK 1 zlwwznto o v TL.D,Lm/6a/1- Patented Sept. 25, 1934 2 UNITED STATES PATENT OFFICE,

22 Claims.

This invention relates to improvements in processes and apparatus for digesting fibrous materials such as wood chips.

The primary object of theinvention is to pro- L3 vide a system whereby air and inert gases contained in the cells of the chips may be removed prior to cooking or at the beginning of the cooking operation.

Another object is to provide a system of the above character in which steam may be admitted while the air and inert gases are being removed for the purpose of initiating dissolving of the water solubles contained in the raw material. By means of my system the chips or the like may be placed in a uniform condition while the air and inert gases alone or in combination with water solubles are removed from the raw material, whereby a much more effective cooking operation is obtained. Furthermore, an operation 20 in accordance with my system gives the raw materlal a thoroughsoaking so that it is in a much more uniform condition as regards moisture content and in a much better shape for the continuance of the cooking operation than is possible without such treatment.

A stillfurther object is to furnish a system whereby a digester after being charged with cellulosic raw material may be completely filled with cooking liquor and a pressure may then be pumped on the digester prior to the time that the liquor is circulated from the digester to the liquor storage tank and from the latter back into i the digester.

A further object is to supply a novel apparatus for accomplishing the above and other new results.

With the above and other objects in view which will appear as the description proceeds, my invention consists in the novel features herein set forth, illustrated in the accompanying drawing and more particularly pointed out in the appended claims;

The drawing shows a diagrammatic view of my improved apparatus.

In the drawing, 1 designates a digester having a top relief branch 2 and a side relief branch 3, provided, respectively with control valves 4 and 5. 6 designates an air vent pipe having a valve 7. The branches 2: and 3 are connected respectively by pipes 8 and 9 to a relief header 10, and a valve 11 is interposed in the line 8 to control the passage of relief fluids from tine digester to the header.

At this point it may be observed that While I have shown only a single digester, of course the invention is applicable to a plant having one or more digesters,, and each digester will be connected in the same manner to the relief header 10.

Fluids relieved from the digester may be introduced into an acid storage tank 12 in several 9 different ways. For example, a pipe 13 leading from the header may discharge into a drop-leg 14 which discharges into the storage tank and is provided with a control valve 15. In some cases, it maybe necessary or desirable to cool the relief fluids before introducing the same into the acid storage tank, and in this case a portion 16 of the pipe 13 will be provided with a control valve 17 and will lead into a cooler 18 terminating in a drop-leg 19 that discharges into 7 the storage tank. The cooler may be of any suitable type but I prefer to use either a beehive or fully submerged type of cooler, of the kinds usually employed in pulp making plants.

If it is unnecessary to discharge the relief fluids into the header 10, they may be passed to the storage tank directly from the side relief branch 3 by means of a pipe 20 having a control valve 21.

A conduit 22 may be employed to pass acid gas from the storage ,tank to the acid preparation system, not shown.

Steam may be introduced into the digester in several conventional ways. For instance, pipe 34 may have a branch 23 leading to valve controlled nozzles 24 which discharge intothe bottom cone of the digester. Valve controlled branches 26 and 27 may lead respectively into the side and lower end of the bottom-portion of the digester.

' A header 28 for use in charging one or more digesters, with acid liquor, is connected to the acid storage tank by a pipe 29 in which a pump 30 and a valve 31 are interposed, and cooking acid from the header 28 flows to each digester through a conduit 32 having a control valve 33.

In practicing my process with the above described apparatus, the digester after being charged with wood chips or the like, is filled with cold acid from the storage tank 12,- and at this point it may be noted that one or more storage tanks may be used depending upon the capacity of the'plant. While acid is being pumped from the storage tank by the pump 30 through 31, 29, 28, 32 and 33, the valves 5 and 11 are kept closed until the air is discharged through 4, 2, 6 and 7.

As soon as acid gas commences to discharge through the air vent 6, the valve 7 is closed, and then'valve 11 as well as. one or the other or both of the valves 15 and 17 are opened, whereby as the liquor rises in the digester, the acid gas will be discharged into the storage tank through the pipe 14 or cooler 18 or both. As soon as liquor appears at the valve 4, this valve is closed and as the top of the digester is now sealed, the pump 30 is continued in operation for the purpose of pumping liquor into the digester until a desired super-atmospheric pressure is reached in the latter. Such pressure may be from ten to ninety (10 to 90) pounds per square inch, and as soon as the desired predetermined pressure is reached, the valves 4, 5, l1 and 17 are opened and, the liquor is circulated from the digester through 2, 3, 8, 9, 10, 13, 16, 18 and 19 back to the storage tank and from the latter through 31, 30, 29, 28, 32 and 33 into the lower end of the digester. The circulation is maintained normally until it is time to fill the next digester with liquor. Usually it is possible to recirculate the liquor from the acid storage tank through the digester and back to the storage tank for a period of about two hours, although this is dependent upon the cooking schedule and .the number of digesters in the plant. The object of such circulation is to remove air and inert gases contained in the cells of the chips and during such circulation steam may or may not be admitted into the bottomof the digester through any one or more of the branches 23, 26 and 2'7. I prefer to admit as much steam as possible during this period in order to start dissolving the water solubles contained in the raw material, and the pumping around as described places all of the chips in a uniform condition and also removes a large majority of the air and inert gases from the cells of the raw material, thereby achieving a much more effective cooking operation than is obtained when this is not done. During the time that circulation is taking place, the raw material becomes more and more penetrated with theacid and although the effect produced is not as pronounced as when hot acid is used from an accumulator, it still is of a considerable benefit, particularly in removing air, inert gases and some of the water solubles that are dissolved at low temperatures. It also results in soaking the raw 1 material so that it is in a' much more uniform condition as regards moisture content and is in much better shape for the continuance of the cooking operation that follows the recirculation.

When it becomes time to fill another digester with acid, the valve 33 is closed and then steam is admitted through any one or more of the branches 23, 26 and 2'1. Of course if steam is admitted during the recirculation, the admittance of the steam will simply be continued when the recirculation stops.

During the normal cooking when starting with cold acid after the recirculation has ceased, the valves 4, 11 and 17 are opened at the start of the cook, and gas, condensate and some liquor pass over through lines 8, 13, 16 and cooler 18 back to the storage tank, and when the proper time arrives, the top relief valve 4 is closed and the side relief valve 5 is opened, and the side relief liquor passes off through 9, 8, 10, 13, 16, 18 and 19 into the liquor in the storage tank, it being understood that the last mentioned liquor functions to absorb any gases remaining in the relief fluids and to mix with any condensates from such fluids. The side relief valve 5 is normally used until dry gas appears at the top, at which time this valve is closed and the valve 2 is again opened and dry gas is relieved through 2, 8, 10, 13, 16, 18 and 19 back into the storage tank until the contents of the digester are properly cooked. Of course steam is admitted to the bottom of the digester in he normal manner during such cooking pe- If desired, recirculation before the cooking permd may take place, as before stated, without passing any fluid through the cooler18. For example, if valve 17 is closed, the fluid can pass through 4, 2, 8, 11, 10', 13, 15 and 14 to the storage tank or by properly manipulating the valves, the fluid can pass through 5, 3, 21 and 20 to the storage tank.

At this point it may be noted that digesting plants are usually equipped with a cooler 18 and as there is no objection to cooling the fiuids during the circulation, I propose to take advantage of the cooler alreadyin a plant, so as to make it unnecessary to add any more piping or valves. However, in .order to make it apparent that the system may be used with or without the cooler 18, I have shown the additional pipes 14 and 20 with their control valves.

While I have disclosed what I now consider to be a preferred embodiment of the apparatus and some novel methods of utilizing the same, I am aware that various changes may be made in the details of the apparatus and the steps of the process without departing from the spirit of the invention as expressed in the claims.

What I claim and desire to secure by Letters Patent is:

1. In a process of the character described, charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and 1 cooking liquor, and then circulating said cooking liquor from the storage tank through the digester and back into the storage tank.

2. In a process of the character described, charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cooking liquor, then circulating said cooking liquor from the storage tank through the digester and 1 back into the storage tank, and venting air from the digester to the atmosphere during the filling of the digester.

3. In a process ofthe character described, charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and 060king liquor, then circulating said cooking liquor from the storage tank through the digester and back into the storage tank, venting air from the digester during the filling operation until gas appears, and then absorbing said gas in the liquor in the storage tank.

4. In a process of the character described, 13 charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cooking liquor, then circulating said cooking liquor from the storage tank through the digester and back into the storage tank, and pumping a pressure on the digester before circulating said liquor.

5. In a process of the character described, '1 charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cooking liquor, then circulating said cooking liquor from the storage tank through the digester and back into the storage tank, and sealing the top of the digester and pumping a pressure on the digester before circulating the liquor through the digester and storage tank.

6. In a process of the character described, charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cooking liquor, then circulating said cooking liquor from the storage tank through the digester and back into the storage tank, venting gases from the digester during the filling operation, cooling said gases and then introducing the same into the liquor in the storage tank.

7. In a process of the character described, charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cooking liquor, then circulating said cooking liquor from the storage tank through the digester and back into the storage tank, and heating the liquor during such circulation.

8. In a process of the character described, charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cooking liquor, then circulating said cooking liquor from the storage tank through the digester and back into the storage tank, and introducing steam into the liquor and fibrous material in the digester during such circulation.

9. In a process of the character described,

charging a digester with fibrous material, then' pumping relatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cooking liquor, then circulating saidcooking liquor from the storage tank throughthe digester and back into the storage tank, and subsequently cooking the contents of the digester while releasing relief fluids from the same.

10. In a process of the character described,

charging a digester with fibrous material, then pumpingrelatively cool cooking liquor from a storage tank into the digester until the latter is completely filled with fibrous material and cook ing liquor, then circulatingsaid cooking liquor fromthe storage tank through the digester and back into the storage tank, halting such circulation, admitting steam into the digester for cooking said fibrous material, and releasing relief fluids from the digester during the cooking period. .11. In a process of thecharacter described, charging a digester with fibrous material, then pumping relatively cool cooking liquor from a storage tank into the digester untilthe latter is completely filled with fibrous material and cooking liquor, then circulating said cooking liquor from the storage tank through the digester and back into the storage tank, halting the circulation of the liquor, then introducing steam into the digester for cooking said fibrous material, releasing gases from the top of the digester and passing the same into said storage tank, and subsequently releasing fluid from the side of the digester and introducing the same into the storage tank. I

12. In a process of the character described, charging a digester with fibrous material, pumping acid liquor from a storage tank into the digester until the latter is completely filled with fibrous material and liquor, then sealing the top fibrous material and liquor, then sealing the top of the digester and continuing the pumping of liquor into the same until a super-atmospheric pressure is pumped on the digester, then unsealing the top of the digester, pumping the liquor from the storage tank through the digester and back into the storage tank, and discharging air from the digester to the atmosphere during the filling operation.

14. In' a process of the character described, charging a digester with fibrous material, pumping acid liquor from a storage tank into the digester until the latter is completely filled with fibrous material and liquor, then sealing the top of the digester and continuing the pumping of liquor into the same until a super-atmospheric pressure is pumped on the digester, then unsealing the top of the digester, pumping the liquor from the storage tank through the digester and back into the storage tank, venting air from the digester during the first portion of the filling operation, and subsequently passing gases from the top portion of the digester back into the storage tank during the remainder of the filling operation.

15. In a process of the character described, charging a digester with fibrous material, pumping acid liquor from a storage tank into the digester until the latter is completely filled with fibrous material and liquor, afterwards circulating the liquor from the storage tank through the digester and back into the storage tank, discontinuing such circulation, then heating the contents of the digester during the cooking period, releasing relief fluids from the digester during the cooking period, cooling said relief fluids, and introducing the cooled fluids into said storage tank.

16. An apparatus of the character described comprising a digester and an acid storage tank, a valved conduit connecting the lower portion of the digester to said storage tank, a pump interposed in said conduit for pumpingv liquor from the tank into the digester, a valved side relief branch for the digester, a valved top branch for the digester, and means connecting said branches to the storage tank for feeding fluids from the top portion of the digester back into the storage tank.

1'7. An apparatus of the character described, comprising a digester and an acid storage tank,

'a valved conduit connecting the lower portion of the digester to said storage tank, a pump interposed in said conduit for pumping liquor from the tank into the digester, a valved side relief branch for the digester, a valved top branch for the digester, and means connecting said branches to the storage tank for feeding fluids from the top portion of the digester back into the storage tank, the last mentioned means including a cooler.

18. An apparatus of the character described, comprising a digester and an acid storage tank, a valved conduit connecting the lower portion of the digester to said storage tank, a pump interposed in said conduit'for pumping liquor from branch for the digester, a valved top branch for the digester, means connecting said branches to the storage tank for feeding fluids from the top portion of the digester back into the storage tank, and a valved air vent operatively connected wit the top relief branch.

19. An apparatus of the character described, comprising a digester, a storage tank, a valved conduit connecting the storage tank with the lower portion of the digester, a pump interposed in said conduit for forcing acid liquor from the storage tank into the digester, a valved pipe connecting the top of the digester to the storage tank, a cooler interposed in said pipe, a second valved pipe connecting the first mentioned pipe to the storage tank, a third valved pipe connecting the side of the digester to the storage tank, and a fourth pipe joining the third pipe to the first mentioned pipe.

20. In a process of the character described, charging a digester with fibrous material, pumping acid liquor from a storage tank into the digester until the latter is completely filled with fibrous material and liquor, then sealing the top of the digester and continuing the pumping of the liquor into the same until a pressure between 10 and pounds gauge is pumped on the digester, then unsealing the top of the digester, and pumping the liquor from the storage tank through the digester and back into the storage tank.

the tank into the digester, a valved side relief 21. In a process of the character described, charging a digester with fibrous material, pumping acid liquor from a storage tank into the digester until the latter is completely filled with fibrous material and liquor, then sealing the top of the digester and continuing the pumping of the liquor into the same until a pressure between 10 and 90 pounds gauge is pumped on the digester, then unsealing the top of the digester and pumping the liquor from the storage tank through the digester and back into the storage tank, and discharging air from the digester to the atmosphere during the filling operation.

22. In a process of the character described, charging a digester with fibrous material, pumping acid liquor from a storage tank into the digester until the latter is completely filled with fibrous material and liquor, then sealing the top of the digester and continuing the pumping of the liquor into the same until a pressure between 10 and 90 pounds gauge is pumped on the digester, then unsealing the top of the digester and pumping the liquor from the storage tank through the digester and back into the storage tank, venting air from the digester during the first portion of the filling operation, and subsequently passing gases from the top portion of the digester back into the storage tank during the remainder of the filling operation.

THOMAS L. DUNBAR. 

